Reverse proxy handling only takes the first letter of X-Forwarded-Host on Asp.net/Owin

[urhot]

There seems to be an issue with the reverse proxy handling introduced in PR #2196

If the X-Forwarded-Host header is set, the API document is generated incorrectly with the "host" value being set to a single character.

Without X-Forwarded-Host header:

% curl --silent "http://localhost/SwaggerTest1/swagger/v1/swagger.json"|grep "host"
"host": "localhost",

With X-Forwarded-Host header:

% curl --silent -H "X-Forwarded-Host: example.com" "http://localhost/SwaggerTest1/swagger/v1/swagger.json"|grep "host"
"host": "e",

By looking at the code, I assume the problem is the assumption that request.Headers[key] returns a list, while in fact it returns a string:

6734543#diff-db5f97cf1d06cc084f0b03b789e44bcfR41

var baseUrl = request.Headers.ContainsKey("X-Forwarded-Host") ?
                new Uri($"{request.GetHttpScheme()}://{request.Headers["X-Forwarded-Host"].First()}").ToString().TrimEnd('/') :
                new Uri($"{request.GetHttpScheme()}://{request.Host}").ToString().TrimEnd('/');

I've only tested with Owin, and I don't know if the same issue exists without it.

My test environment (a WebAPI project):

OwinStartup.cs:

[assembly: OwinStartup(typeof(SwaggerTest1.OwinStartup))]
namespace SwaggerTest1
{
    public class OwinStartup
    {
        public void Configuration(IAppBuilder app)
        {
            app.UseSwaggerUi3(typeof(OwinStartup).Assembly, settings => {
            });

            if (HostingEnvironment.IsHosted) {
                GlobalConfiguration.Configure(ConfigureWebApi);
            } else {
                var config = new HttpConfiguration();
                ConfigureWebApi(config);
                app.UseWebApi(config);
            }
        }

        public static void ConfigureWebApi(HttpConfiguration config)
        {
            config.Formatters.XmlFormatter.SupportedMediaTypes.Clear();

            config.MapHttpAttributeRoutes();
            config.EnsureInitialized();
        }
    }
}

NuGet packages:

PM> get-package
Id                                  Versions  ProjectName                                                                                                                        
--                                  --------  -----------                                                                                                                        
Microsoft.AspNet.WebApi             {5.2.4}   SwaggerTest1                                                                                                                       
Microsoft.AspNet.WebApi.Client      {5.2.7}   SwaggerTest1                                                                                                                       
Microsoft.AspNet.WebApi.Core        {5.2.7}   SwaggerTest1                                                                                                                       
Microsoft.AspNet.WebApi.Owin        {5.2.7}   SwaggerTest1                                                                                                                       
Microsoft.AspNet.WebApi.WebHost     {5.2.4}   SwaggerTest1                                                                                                                       
Microsoft.CodeDom.Providers.DotN... {2.0.0}   SwaggerTest1                                                                                                                       
Microsoft.Owin                      {4.0.1}   SwaggerTest1                                                                                                                       
Microsoft.Owin.FileSystems          {3.0.1}   SwaggerTest1                                                                                                                       
Microsoft.Owin.Host.SystemWeb       {4.0.1}   SwaggerTest1                                                                                                                       
Microsoft.Owin.StaticFiles          {3.0.1}   SwaggerTest1                                                                                                                       
Namotion.Reflection                 {1.0.6}   SwaggerTest1                                                                                                                       
Newtonsoft.Json                     {11.0.1}  SwaggerTest1                                                                                                                       
NJsonSchema                         {10.0.22} SwaggerTest1                                                                                                                       
NSwag.Annotations                   {13.0.5}  SwaggerTest1                                                                                                                       
NSwag.AspNet.Owin                   {13.0.5}  SwaggerTest1                                                                                                                       
NSwag.Core                          {13.0.5}  SwaggerTest1                                                                                                                       
NSwag.Generation                    {13.0.5}  SwaggerTest1                                                                                                                       
NSwag.Generation.WebApi             {13.0.5}  SwaggerTest1                                                                                                                       
Owin                                {1.0}     SwaggerTest1     

[urhot]

[RicoSuter]

Its probably a diff between owin and aspnetcore (string vs string[])